1. Field of the Invention
The present invention relates to a locking mechanism for a utility knife, and more particularly to a quick release locking mechanism for a utility knife, wherein the locking mechanism may be used with a utility knife having a metal housing or may be integral with the blade carrier and/or return spring in an automatically retractable utility knife.
2. Description of the Related Art
Utility knives are well known in the art, and typically include a housing, which is often constructed of separable halves, a blade carrier, which holds a razor or other blade, and a handle or thumb piece attached to the blade carrier and extending from the housing to enable the blade to be extended from and retracted into the housing. Utility knives are available in automatically retractable and indexed versions.
In an automatically retractable utility knife, a spring is attached between the housing and the blade carrier to automatically retract the blade into the housing upon release of the thumb piece. The spring tension is such that when the blade is projected and inserted in a material being cut, e.g., cardboard, the friction between the blade and the material is sufficient to retain the blade in the projected position. In an indexed utility knife, the blade may be moved between one of several locked positions, including fully retracted and fully extended positions.
In many utility knives, the housing is constructed of two halves which are attached by means of a screw located toward the center of the housing. In order to replace the blade, it is necessary to unscrew the halves of the housing, which requires a screwdriver, and which is both time consuming and inconvenient. To overcome this shortcoming, utility knives with plastic housings have been developed that incorporate a locking mechanism that may be released without tools. For example, U.S. Pat. No. 5,121,544 relates to a utility knife that is constructed of separable plastic halves and that includes a rear snap-locking mechanism. In order to operate the locking mechanism, the user must push an actuating lever and slide the halves in opposite directions generally parallel to a central axis of the housing, i.e., generally parallel to the direction of movement of the blade, before the halves release from each other.
Commonly-owned U.S. Pat. Nos. 6,058,607 and 5,813,121, the contents of which are incorporated herein by reference, disclose a utility knife locking mechanism that includes a resilient locking arm on a first half of the housing, and a locking aperture on the other half of the housing. In use, the locking arm is pushed into the locking aperture to lock the halves of the housing together. When the locking arm is depressed, it becomes released from the locking aperture to allow the housing to be opened.
Quick-release locking mechanisms of this type have been utilized only in plastic knives, in which the locking mechanism may be molded integrally with the housing, and in which the materials are sufficiently flexible to enable the locking arm to be released. Such locking mechanisms have not been used in metal housings, since the metals used are often too rigid to be used in the locking mechanism.
Accordingly, it would be desirable to have a quick-release locking mechanism for a utility knife that may be used with knife having a metallic housing. More generally, it would be desirable to have a quick-release locking mechanism for a utility knife that is separable from the housing itself so that the locking mechanism may be used with housings constructed of materials unsuitable for being constructed integral with the locking mechanism.